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Question

I want to check if the username already exists and throw an error message if exist, any tips how can I do it? I\'ve already tried to search but only found mys

Answer 1

Two solutions:

You could make the username field unique, this way, MYSQL would throw an error if you try to insert a line with an existing username.

$sql = "INSERT INTO users (username,password,role) values(?, ?, ?)";
$q = $pdo->prepare($sql);
$result = $q->execute(array($username,$password,$role));
if(!$result) {
    // print out your error message
}

Otherwise, make a select with the wanted username and see if a row is returned (= already used) or not (=available).

$sql = "SELECT COUNT(*) as count FROM users WHERE username = ?";
$q = $pdo->prepare($sql);
$q->execute(array($username));
$result = $q->fetchAll();
// test result, if 1 > print error, etc

Answer 2

 <?php
     $getUniqueUsername=$con->query("select * from user where name='$user_name");
     $rowCount=$getUniqueUsername->num_rows;

     if($rowCount) {          
          $insertQuery=$con->query("insert into table_name (field_name) Values('".$values."'));
     }
?>

Answer 3

SELECT * FROM users WHERE username = $username

If found show error, else insert

Answer 4

If you want to check if the username is already used :

SELECT * FROM users WHERE username = :username

If you return one row : you throw your error, else you do your INSERT

So your code should look like this :

if ($valid) {
    $pdo = Database::connect();
    $pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);

    $sql_check = "SELECT * FROM users WHERE username = :username";
    $test = $pdo->prepare($sql_check);
    $test->bindParam(':username', $username); 
    $test->execute;

Now here is two solution to check if you have one row :

    if($test->rowCount() > 0) {
        // error
    }      

or

    $user = $test->fetch();

    if (!empty($user)) {
        // error
    }

And now if you don't have error, do you insert :

    else {
        //$password = md5($password);
        $sql = "INSERT INTO users (username,password,role) values(?, ?, ?)";
        $q = $pdo->prepare($sql);
        $q->execute(array($username,$password,$role));
        Database::disconnect();
        header("Location: index.php");
    }
}